Another great blog post on great research by the DeepMind guys, who are also simultaneously releasing a new dataset for long-range language modeling.
The post is worth reading in its entirety.
If I may summarize, the authors propose a transformer augmented with a short-term memory mechanism (analogous to TransformerXL) as well as a long-term memory mechanism (new) that learns to 'compress and memorize' embeddings from the short-term memory. The model is trained on book-length samples (!!!!), and seems to perform significantly better than prior models at generating language with long-range contexts. To my eyes, text generated by the trained model is virtually indistinguishable from human output, and qualitatively superior to GPT2 samples.